Understand, model and exploit the acoustic propagation physics in shallow water in the presence of ocean fronts and internal waves. This goal conforms to the major theme of the Shallow Water 06 experiment i.e. 3-D acoustic effects. The effects of oceanographic variability such as frontal meander, and internal solitary waves on 3-D acoustic reflection and refraction will be investigated. Improve inversion schemes for the estimation of sediment geoacoustic properties using low frequency broadband acoustic signals. Improve our long range sediment tomography technique for compressional wave speed and attenuation profiles and utilize a new broadband Combustive Sound Source (CSS) developed at the Applied Research Laboratories (ARL), University of Texas. The existing inversion method has been shown to successfully map compressional wave speed. The new work will focus on understanding the frequency and depth dependence of compressional wave attenuation and develop new inversion schemes for shear wave properties. We hypothesize that water-borne acoustic arrival properties such as their Airy Phase are sensitive to sediment shear properties. We hope to validate this hypothesis over the next period of investigation.